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Note: the following discussion and proceduft~s are abstracted from material provided by the Colorado School of Mines; original can be found at: http: /Mrww.mines.edu/fs_homelhoran/cht26/app.htm Acid Producing Potential of Mine Overburden P~ECEIVED FEB 2 7 ?.007 Division of ~feclamation, Mining and Safety Introduction Mine overburden and waste soils (commonly referred to as mine tailings) are the waste products generated tluring mining and milling operations. Surface deposition of these waste products results in exposure !o the atmosphere, predpitation, and ground or aurtace water. Many of tlrese tailings possess the potential to react with oxygen and water genereting products that adversety affect the pH and heavy metal composition of nearby eels and streams. The generation of add mine drainage can also be iMluenced by the biological activity of microorganisms. Mining of ~ and predous metals has left large volumes of mining overburden and waste soils throughout the Unfted States. Many of these tailings are now causing problems with water quality and revegetation. The EPA and individual states have now taken action to dean up problem areas and to prevem further environmental degradation from proposed mining projects. In order to determine the moat effective methotl to dean up existing ekes and as part of the regulatory process for land disposal of mine overburden, testing must be performed to determine the potential add generating materials in the tailings, A preliminary step is to determine the Aad Producing Potential (APP) of the mine overburden and waste material. Add Base Accounting is a static procedure that can be used to predict if a sample mine overburden material will bean add producer or a neutralizer. The add produdng potential in a rock is dad directly to the amount of sulfides bountl up in the rode in various forms. Sulfides are crystalline substances that contain sulfur combined with a metal or semi-metal, but no oxygen. The moat common forms are Pyrite and Marcasite (FeS2). Other forms indude Fe,_„S,,, Fe3S~, FeS, CuFeS4, ZnS, PbS, HgS, and CoAsS. When these sulfide minerals in mine overburden weather upon exposure to water and air, toxic metal ions and hydrogen ions are released into the environmem. The sulfide ion is oxidized into soluble auHate ions. Since pyrite is the most common mineral in mine tailings, iron III ions are released in rather high concentrations. In acidic runoff (<pH 3), the iron ions are soluble. The pH of acidic runoff from mine tailings will usually increase as a result of dilution from other water sources. This increase in pH causes soluble iron ions to precipitate out of solution in the forth of iron III hydroxide, a gelatinous, reddish-orange edict. This precpitate called "yellow boy" coats the bottom of the stream creating an unsightty and unnatural condition in the riparian environment.